Field of the Invention
The present invention relates to a distance measuring system suitable for measuring a distance of a target from the system, and in particular a compact, lightweight and economical construction of such a system.
Short Description of the Related Prior Art
A plurality of technologies is available for determining the distance of a target from the distance measuring system.
These technologies usually contain the emitting of radiation (e.g., optical radiation, ultrasound and radar) in the direction of the target and a receiving of a part of the radiation reflected back from the target. The distance from the system to the target is determined by one of several approaches familiar to the person skilled in the art; therefore, a detailed description will be dispensed with. A few examples are described in the documents U.S. Pat. No. 4,113,381, U.S. Pat. No. 5,241,360, U.S. Pat. No. 6,765,653 or US 2004/0246461. For example, some systems calculate the distance from the system to the target by determining a phase difference between radiation emitted to the target and reflected radiation received from the target, whereas, on the other hand other systems measure a time difference between the emission of the radiation to the target and between the reception of the reflected radiation on the system. For example, the measuring of the distance can take place by emitting a modulated microwave carrier signal or modulated optical carrier signal, which signal is reflected by the target. The distance can then be determined, for example, by emitting and receiving multiple frequencies and by determining the integer number of wavelengths to the target for each frequency.
The target can be a so-called “non-cooperative target” that has a comparatively low reflectivity for the particular radiation (a wall of a building, a stone, a tree or another object in the environment). Such a non-cooperative target is also designated as a “DR (direct reflex) target”. Alternatively, the target can be a so-called “cooperative target” that has a comparatively high reflectivity for the particular radiation (for example, a prism or a reflector). Such a cooperative target is also designated as a “PR (prism reflex) target”.
Distance measuring systems that use optical radiation customarily comprise a radiation source, a radiation detector and a measuring lens system in order to project optical radiation emitted by the radiation source to the target and to guide optical radiation reflected by the target back to the radiation detector. In order to adapt the radiation detector to changing intensities of the optical radiation that is reflected from the different targets and received by the radiation detector, the systems furthermore frequently comprise a variable damper in order to adapt the intensity of the optical radiation incident on the radiation detector. Since radiation detectors with an inner gain (amplification) for optical radiation are subject to a certain temperature drift, the systems furthermore frequently comprise a reference lens system/reference optics and an optical switch in order to directly guide optical radiation generated by the radiation source and conducted via a previously known reference stretch/reference distance to the radiation detector and thus make possible a scaling of the radiation detector regarding reinforcement and drift.